[Xen-devel] iommu=dom0-passthrough behavior

["Jan Beulich" <JBeulich@xxxxxxxx>]

All,

so far it was my understanding that this option is intended to get
the DMA behavior that Dom0 observes as close as possible to how
it would be without IOMMU.

However, we're now dealing with a customer report where a
single function device is observed to initiate DMA operations
appearing to originate from function 1, which makes obvious that
the option above is not making things as transparent as I would
have expected them to be: Without IOMMU, such requests get
processed fine, while with IOMMU (due to there not being a
context entry for the bogus device) the device fails to initialize
(causing DMA faults, the presence of which I had to convince
myself of separately, as for whatever reason at least the VT-d
code doesn't issue any log message in that case).

So I'm now seeking for alternative workaround suggestions that
we could pass to that customer (less intrusive than "iommu=off").

Thanks, Jan


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